Background. Recent epidemiological studies in inflammatory bowel disease (IBD) indicate that paediatric onset of IBD (pIBD) more often requires biological therapy compared to adult onset of IBD (aIBD). Whether this is due to a more aggressive disease phenotype or lower threshold of prescribing biologicals is unknown. In order to expand these findings in a clinical setting, we compared the inflammatory burden in pIBD and aIBD patients requiring biological therapy. Methods. We retrospectively included 70 pIBD and 83 aIBD patients initiating biological therapy. Symptoms and biomarker levels were recorded prior to and 6, 14, 22, and 52 weeks after initiation of biological therapy. Results. In Crohn’s disease (CD), the baseline levels of faecal calprotectin and C-reactive protein (CRP) were increased in paediatric CD patients compared to adult CD patients ( and , respectively). No significant differences were seen in ulcerative colitis (UC). In CD, baseline vitamin D  nmol/L and baseline CRP  mg/L were associated with higher remission rate () at the end of follow-up. Moreover, aIBD patients had a higher risk of loss of response to biological therapy and treatment discontinuation compared to pIBD patients ( [1.6-13.4], ). Conclusions. pCD patients had increased inflammation markers compared to aCD patients prior to biological treatment. In addition to this,  nmol/L and high CRP levels predicted poor response to treatment in IBD patients.